Novel compounds of the N-acylamino amide family, compositions comprising them and uses thereof

ABSTRACT

The invention concerns novel compounds of the N-acylamino-amide family, compositions, in particular cosmetic or pharmaceutical, containing them, and their use for treating body or face skin ageing, whether chronobiologic or light-induced, and in particular skin ageing caused by decrease of skin elasticity and/or by collagen degradation in the structure of tissues.

The present invention relates to novel compounds of the N-acylamino amide family, to their use in particular in cosmetics or in pharmaceuticals, and to compositions comprising them.

Human skin consists of two compartments, i.e. a superficial compartment, the epidermis, and a deep compartment, the dermis.

Natural human epidermis is composed mainly of three types of cell: the keratinocytes, which form the vast majority, the melanocytes and the Langerhans cells. Each of these cell types contributes, by virtue of its intrinsic functions, towards the essential role played in the body by the skin.

The dermis gives the epidermis a solid support. It is also the epidermis' nourishing factor. It consists mainly of fibroblasts and of an extracellular matrix itself composed mainly of collagen, elastin and a substance, known as ground substance, these components being synthesized by the fibroblast. Leukocytes, mastocytes and tissue macrophages are also found in the dermis. Finally, the dermis contains blood vessels and nerve fibres.

It is known that during a superficial cutaneous stress, which may in particular be of chemical, physical or bacterial origin, the keratinocytes of the superficial layers of the epidermis release biological mediators which have the ability to attract certain cells which infiltrate the skin, which are themselves responsible for maintaining transient local irritation.

Among the biological mediators which may be produced by the keratinocytes thus stressed, mention may be made of chemokines, which are chemoattractant cytokines that are responsible for recruiting leukocytes to the sites of inflammation, including interleukin 8 (IL-8) which is more particularly responsible for recruiting neutrophils.

These cells infiltrating the irritated or attacked areas then release enzymes, among which mention may be made of leukocyte elastase.

Due in particular to the action of this enzyme, the extracellular supporting elastic fibres of the connective tissue may be degraded, and thus result in a reduction in the elasticity of the skin.

It is even furthermore known that, in synergy with cathepsin G, leukocyte elastase may dissociate the integrity of the epidermis by widening the inter-keratinocyte intercellular spaces.

Thus, in the long-term, the sum of the superficial cutaneous micro-stresses, for example generated by a prolonged exposure to UV or by irritant agents, may result in a more or less accelerated loss of the skin's natural elasticity. The network formed by the elastic fibres of the underlying connective tissue and of the extracellular spaces may then be gradually destructured. This results in accelerated ageing of the skin (wrinkled and/or less supple skin) via the impairment of the dermal elastic network, and also an accentuation of the wrinkles (deeper wrinkles).

Moreover, it is known that the firmness of the dermis is mainly ensured by the collagen fibres. These fibres consist of fibrils sealed together, thus forming more than ten different types of structure. The firmness of the dermis is largely due to the overlapping of the collagen fibres packed together in all directions. The collagen fibres play a part in the elasticity and tonicity of the skin and/or the mucous membranes.

The collagen fibres are constantly being renewed, but this renewal diminishes with age, resulting in a thinning of the dermis. This thinning of the dermis is also due to pathological causes such as, for example, the hypersecretion of corticoid hormones, certain pathologies or vitamin deficiencies (in the case of vitamin C in scurvy). It is also accepted that extrinsic factors such as ultraviolet rays, tobacco or certain treatments (glucocorticoids, vitamin D and derivatives, for example) also have an effect on the skin and on its collagen content.

Although very strong, collagen fibres are sensitive to certain enzymes known as collagenases. A degradation of the collagen fibres results in the appearance of flaccid and wrinkled skin, which people, preferring the appearance of smooth and taut skin, have always endeavoured to combat.

Moreover, at the menopause, the main changes regarding the dermis are a decrease in the collagen content and in the thickness of the dermis. In menopausal women, this results in a thinning of the skin and/or of the mucous membranes. Women then experience a “dry skin” sensation or a sensation of skin under tension, and an accentuation of the surface lines and fine wrinkles is observed. The skin has a coarse appearance when touched. Finally, the suppleness of the skin is reduced.

One aim of the present invention is to propose a solution to these various problems, and in particular to propose novel compounds which may be used in cosmetics or in pharmaceuticals to limit the ageing of the skin, whether chronobiological or light-induced ageing, and in particular the ageing generated by a reduction in the elasticity of the skin and/or by a degradation of the collagen in the structure of the tissues.

Without being bound by the present explanation, it may be considered that the fact of providing, to the keratinocytes of the surface layers of the skin, compounds capable of slowing down the degradation activity of the elastic fibres of the intercellular spaces, may make it possible to reduce this phenomenon of accelerated ageing of the skin, due to superficial cutaneous stresses.

Certain compounds belonging to the family of N-acylamino amides are known in the prior art. Examples that may be mentioned include the docoment J. Am. Chem. Soc., 1977, 99(18), pp. 6075-82) which describes a process for synthesizing the following derivatives:

-   N-acetylglycyl-N-(benzyl)-DL-valylglycine tert-butyl ester; -   N-acetylglycyl-N-(2-nitrobenzyl)-DL-valylglycine tert-butyl ester; -   N-acetylglycyl-N-(2,4-dimethyloxybenzyl)-DL-valylglycine tert-butyl     ester.

One subject of the present invention is thus a compound of formula (I) as defined below, with the exception of the following derivatives:

-   N-acetylglycyl-N-(benzyl)-DL-valylglycine tert-butyl ester; -   N-acetylglycyl-N-(2-nitrobenzyl)-DL-valylglycine tert-butyl ester; -   N-acetylglycyl-N-(2,4-dimethyloxybenzyl)-DL-valylglycine tert-butyl     ester.

A subject of the invention is also a composition comprising, in a physiologically acceptable medium, at least one such compound of formula (I).

Another subject of the invention is the use of at least one compound of formula (I), or of a composition comprising it, to treat, preventively or curatively, the signs of ageing of facial or body skin, whether chronobiological or light-induced ageing, and in particular the ageing generated by a reduction in the elasticity of the skin and/or by a degradation of the collagen in the structure of the tissues.

Another subject of the invention is the use of at least one compound of formula (I), or of a composition comprising it, to treat, preventively or curatively, wrinkles and/or fine lines, wizened skin, a lack of elasticity and/or of tonus of the skin, thinning of the dermis, the degradation of collagen fibres, flaccid skin and thinned skin; the internal degradation of the skin following exposure to ultraviolet radiation.

Another subject of the invention is the use of at least one compound of formula (I), or of a composition comprising it, to inhibit the activity of elastases and/or to limit and/or combat the degradation of the elastic fibres.

Another subject of the invention is a cosmetic treatment process for facial or body skin, including the scalp, in which a cosmetic composition as defined below is applied to the skin.

Specifically, it has been found that the compounds of formula (I) have inhibitory activity on the activity of elastases, and that they may thus be used to limit and/or combat the degradation of the elastic fibres.

It follows therefrom that they may be used in or for the preparation of a composition, the compounds or the composition being intended to treat, preventively and/or curatively, the signs of ageing of the skin.

The expression “signs of ageing of the skin” means any changes in the outer appearance of the skin that are due to ageing, whether chronobiological and/or light-induced ageing, such as, for example, wrinkles and fine lines, wizened skin, a lack of elasticity and/or of tonus of the skin, thinning of the dermis and/or degradation of the collagen fibres which results in the appearance of flaccid and wrinkled skin; it is also understood to mean any internal changes in the skin which are not automatically reflected by a changed outer appearance, such as, for example, all internal degradations of the skin, particularly of the elastin fibres, or elastic fibres, following exposure to ultraviolet radiation.

One advantage of the present invention lies in the fact that the compounds of formula (I) may be readily prepared.

The compounds which may be used in the present invention thus correspond to formula (I) below:

in which:

-   -   the radical Y represents O or S,     -   the radical R1 represents:         -   (i) a hydrogen atom;         -   (ii) a linear, branched or cyclic, saturated or unsaturated             hydrocarbon-based radical containing 1 to 18 carbon atoms,             optionally substituted with 1 to 5 groups, which may be             identical or different, chosen from —OH; —OR; —O—COR; —SH;             —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen);             —CN; —COOR; —COR; —P(O)—(OR)₂; —SO₂—OR; with R and R′             representing, independently of each other, a linear,             branched or cyclic, saturated or unsaturated             hydrocarbon-based radical containing 1 to 6 carbon atoms,             which is optionally halogenated, or even perhalogenated,             the said radicals R and R′ possibly forming together with N             a 5- or 6-membered carbon-based ring which may also comprise             at least one hetero atom chosen from O, N and/or S in the             ring, and/or which may be substituted with 1 to 5 groups,             which may be identical or different, chosen from —OH; —OR″;             —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal             (halogen); —CN; —COOR″; —COR″; with R″ representing a             linear, branched or cyclic, saturated or unsaturated             hydrocarbon-based radical containing 1 to 6 carbon atoms,             which is optionally halogenated, or even perhalogenated;     -   (iii) a radical chosen from the following radicals: —OR; —NH₂;         —NHR; —NRR′; —NH—COR; —COOR; —COR; with R and R′ representing,         independently of each other, a linear, branched or cyclic,         saturated or unsaturated hydrocarbon-based radical containing 1         to 6 carbon atoms, which is optionally halogenated, or even         perhalogenated,         the said radicals R and R′ possibly forming together with N a 5-         or 6-membered carbon-based ring which may also comprise at least         one hetero atom chosen from O, N and/or S in the ring, and/or         which may be substituted with 1 to 5 groups, which may be         identical or different, chosen from —OH; —OR″; —O—COR″; —SH;         —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN;         —COOR″; —COR″; with R″ representing a linear, branched or         cyclic, saturated or unsaturated hydrocarbon-based radical         containing 1 to 6 carbon atoms, which is optionally halogenated,         or even perhalogenated;     -   the radical R2 represents a linear, branched or cyclic,         saturated or unsaturated hydrocarbon-based radical containing 1         to 18 carbon atoms, optionally substituted with 1 to 5 groups,         which may be identical or different, chosen from —OH; —OR;         —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal         (halogen); —CN; —COOR; —COR;         with R and R′ representing, independently of each other, a         linear, branched or cyclic, saturated or unsaturated         hydrocarbon-based radical containing 1 to 6 carbon atoms, which         is optionally halogenated, or even perhalogenated,         the said radicals R and R′ possibly forming together with N a 5-         or 6-membered carbon-based ring which may also comprise at least         one hetero atom chosen from O, N and/or S in the ring, and/or         which may be substituted with 1 to 5 groups, which may be         identical or different, chosen from —OH; —OR″; —O—COR″; —SH;         —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN;         —COOR″; —COR″; with R″ representing a linear, branched or         cyclic, saturated or unsaturated hydrocarbon-based radical         containing 1 to 6 carbon atoms, which is optionally halogenated,         or even perhalogenated;     -   the radical R3 represents a radical chosen from those of         formula (II) or (III):         -A-C₆H_((5-y))—B_(y)  (II)         —C₆H_((5-y′))—B_(y)′  (III)         in which:         -   y is an integer between 0 and 5 inclusive and y′ is an             integer between 1 and 5 inclusive;         -   A is a linear or branched, saturated or unsaturated divalent             hydrocarbon-based radical containing 1 to 18 carbon atoms,             optionally substituted with 1 to 5 groups, which may be             identical or different, chosen from —OH; —OR; —O—COR; —SH;             —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen, or             even perhalogen); —CN; —COOR; —COR; —NO₂; —SO₂—OR;             with R and R′ representing, independently of each other, a             linear, branched or cyclic, saturated or unsaturated             hydrocarbon-based radical containing 1 to 6 carbon atoms,             which is optionally halogenated, or even perhalogenated, the             said radicals R and R′ possibly forming together with N a 5-             or 6-membered carbon-based ring which may also comprise at             least one hetero atom chosen from O, N and/or S in the ring,             and/or which may be substituted with 1 to 5 groups, which             may be identical or different, chosen from —OH; —OR″;             —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal             (halogen); —CN; —COOR″; —COR″; with R″ representing a             linear, branched or cyclic, saturated or unsaturated             hydrocarbon-based radical containing 1 to 6 carbon atoms,             which is optionally halogenated, or even perhalogenated;     -   B represents at least one group, which may be identical or         different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂;         —NHR; —NRR′; —NH—COR; -Halogen; —CN; —COOR; —COR; —NO₂; —SO₂—OR,         or represents a linear or branched, saturated or unsaturated         hydrocarbon-based radical containing 1 to 18 carbon atoms,         optionally substituted with 1 to 5 groups, which may be         identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR;         —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen, or even         perhalogen); —CN; —COOR; —COR; —NO₂; —SO₂—OR;         with R and R′ representing, independently of each other, a         linear, branched or cyclic, saturated or unsaturated         hydrocarbon-based radical containing 1 to 6 carbon atoms, which         is optionally halogenated, or even perhalogenated,         the said radicals R and R′ possibly forming together with N a 5-         or 6-membered carbon-based ring which may also comprise at least         one hetero atom chosen from O, N and/or S in the ring, and/or         which may be substituted with 1 to 5 groups, which may be         identical or different, chosen from —OH; —OR″; —O—COR″; —SH;         —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN;         —COOR″; —COR″; with R″ representing a linear, branched or         cyclic, saturated or unsaturated hydrocarbon-based radical         containing 1 to 6 carbon atoms, which is optionally halogenated,         or even perhalogenated;     -   the radical X represents a radical chosen from —OH, —OR₄, —NH₂,         —NHR₄, —NR₄R₅, —SR₄, —COOR₄ and —COR₄; with R₄ and R₅         representing, independently of each other, a linear, branched or         cyclic, saturated or unsaturated hydrocarbon-based radical         containing 1 to 6 carbon atoms, optionally substituted with 1 to         5 groups, which may be identical or different, chosen from —OH;         —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal         (halogen, or even perhalogen); —CN; —COOR; —COR; with R and R′         representing, independently of each other, a linear, branched or         cyclic, saturated or unsaturated hydrocarbon-based radical         containing 1 to 6 carbon atoms, which is optionally halogenated,         or even perhalogenated, the said radicals R and R′ possibly         forming together with N a 5- or 6-membered carbon-based ring         which may also comprise at least one hetero atom chosen from O,         N and/or S in the ring, and/or which may be substituted with 1         to 5 groups, which may be identical or different, chosen from         —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″;         -Hal (halogen); —CN; —COOR″; —COR″; with R″ representing a         linear, branched or cyclic, saturated or unsaturated         hydrocarbon-based radical containing 1 to 6 carbon atoms, which         is optionally halogenated, or even perhalogenated;         the said radicals R₄ and R₅ possibly forming together with N a         5- or 6-membered carbon-based ring which may also comprise at         least one hetero atom chosen from O, N and/or S in the ring,         and/or which may be substituted with 1 to 5 groups, which may be         identical or different, chosen from —OH; —OR″; —O—COR″; —SH;         —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN;         —COOR″; —COR″; with R″ representing a linear, branched or         cyclic, saturated or unsaturated hydrocarbon-based radical         containing 1 to 6 carbon atoms, which is optionally halogenated,         or even perhalogenated,         with the exception of the following derivatives:

-   N-acetylglycyl-N-(benzyl)-DL-valylglycine tert-butyl ester;

-   N-acetylglycyl-N-(2-nitrobenzyl)-DL-valylglycine tert-butyl ester;

-   N-acetylglycyl-N-(2,4-dimethyloxybenzyl)-DL-valylglycine tert-butyl     ester.

Also included in this definition are the mineral acid or organic acid salts of the said compounds, and also the optical isomers thereof, in isolated form or as a racemic mixture.

The expression “linear, branched or cyclic hydrocarbon-based radical” in particular means radicals of alkyl, aryl, aralkyl, alkylaryl, alkenyl or alkynyl type.

The C₆H₅ group present in the radical R3 should be understood as being a cyclic aromatic group.

The radical Y preferably represents oxygen.

Preferably, the radical R1 represents hydrogen or a linear or branched, saturated or unsaturated, optionally substituted hydrocarbon-based radical containing 1 to 12 and in particular 1, 2, 3, 4, 5 or 6 carbon atoms.

In particular, the substituents may be chosen from —OH, —OR and/or —P(O)—(OR)₂ with R representing a linear, branched or cyclic, saturated or unsaturated hydrocarbon-based radical containing 1 to 6 carbon atoms, which is optionally halogenated, or even perhalogenated.

The radical R1 preferably represents a methyl, ethyl, propyl or isopropyl radical, optionally substituted with a group —OH or —P(O)—(OR)₂ with R representing methyl, ethyl, propyl or isopropyl.

Preferably, the radical R2 represents a linear, branched or cyclic, saturated or unsaturated, optionally substituted hydrocarbon-based radical containing 1 to 12 and in particular 1, 2, 3, 4, 5 or 6 carbon atoms.

In particular, the substituents may be chosen from —OH and —OR with R representing a linear, branched or cyclic, saturated or unsaturated hydrocarbon-based radical containing 1 to 6 carbon atoms, which is optionally halogenated, or even perhalogenated.

The radical R2 preferably represents a methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl or isobutyl radical.

The radical R3 preferably represents a radical of formula —C₆H_((5-y′))—B_(y)′ for which y′=1, 2 or 3; or a radical of formula -A-C₆H_((5-y))—B_(y) for which y=0, 1 or 2. Preferably, A is a linear or branched, saturated or unsaturated, optionally substituted divalent hydrocarbon-based radical containing 1 to 12 carbon atoms.

The substituents of A are preferably chosen from -Hal (halogen, or even perhalogen); —CN; —COOR; —NO₂; —SO₂—OR; with R representing a linear, branched or cyclic, saturated or unsaturated hydrocarbon-based radical containing 1 to 6 carbon atoms, which is optionally halogenated, or even perhalogenated.

Preferably, B represents at least one group —OR; —NHR; —CN; —COOR; —COR or represents a hydrocarbon-based radical chosen from a linear or branched, saturated or unsaturated, optionally substituted hydrocarbon-based radical containing 1 to 12 carbon atoms.

The substituents of B are preferably chosen from -Hal (halogen, or even perhalogen); —CN; —COOR; —NO₂; —SO₂—OR; with R representing a linear, branched or cyclic, saturated or unsaturated hydrocarbon-based radical containing 1 to 6 carbon atoms, which is optionally halogenated, or even perhalogenated.

The radical R3 preferably represents a group chosen from one of the following formulae:

in which A and B have the above meanings.

In particular, the divalent radical A may be a methylene, an ethylene or a propylene.

Preferably, the radical B represents at least one group —OR; —NHR; —CN; COOR; —COR for which R denotes a methyl, ethyl, propyl or isopropyl radical or represents a hydrocarbon-based radical chosen from a methyl, ethyl, propyl or isopropyl radical, substituted with one or more halogens, in particular chlorine, bromine, iodine or fluorine, and preferably totally halogenated (perhalogenated), such as perfluorinated. Mention may be made in particular of the perfluoromethyl radical (—CF₃) as being most particularly preferred.

Preferably, the radical X represents a radical chosen from —OH and —OR₄ with R₄ representing a linear, cyclic or branched, saturated or unsaturated hydrocarbon-based radical containing 1 to 6 carbon atoms, which is optionally substituted.

The substituents may be chosen from —OH and —OR with R representing a linear, branched or cyclic, saturated or unsaturated hydrocarbon-based radical containing 1 to 6 carbon atoms, which is optionally halogenated, or even perhalogenated.

Preferably, the radical X represents a radical chosen from —OH, —OCH₃, —OC₂H₅, —O—C₃H₇ and —OC₄H₉.

Among the compounds that are particularly preferred, mention may be made of:

-   {2-[acetyl(3-trifluoromethylphenyl)amino]-3-methylbutyrylamino}acetic     acid, -   ethyl     {2-[acetyl(3-trifluoromethylphenyl)amino]-3-methylbutyrylamino}acetate, -   [2-(acetylbenzylamino)-3-methylbutyrylamino]acetic acid, -   ethyl [2-(acetylbenzylamino)-3-methylbutyrylamino]-acetate, -   ethyl     (2-{benzyl[(diethoxyphosphoryl)acetyl]amino}-3-methylbutyrylamino)acetate.

The compounds according to the invention may be readily prepared by a person skilled in the art on the basis of his general knowledge. In particular, a carboxylic acid, an aldehyde, an amine compound and an isonitrile may be reacted together in an Ugi reaction.

Needless to say, during the synthesis of the compounds according to the invention, and depending on the nature of the various radicals present on the starting compounds, a person skilled in the art may take care to protect certain substituents so that they do not participate in the rest of the reactions.

The amount of compound to be used in the compositions according to the invention may be readily determined by a person skilled in the art, as a function of the nature of the compound used, the individual to be treated and/or the desired effect. In general, this amount may be between 0.00001% and 20% by weight relative to the total weight of the composition, in particular between 0.001% and 10% by weight, preferably between 0.05% and 5% by weight, better still between 0.1% and 2% by weight and preferentially between 0.5% and 1% by weight.

The compounds of formula (I) may be used in particular, alone or as a mixture, in a composition which comprises a physiologically acceptable medium, in particular in a cosmetic or pharmaceutical composition which thus moreover comprises a cosmetically or pharmaceutically acceptable medium.

The physiologically acceptable medium in which the compounds according to the invention may be used, and the constituents thereof, the amount thereof, the presentation form of the composition and its method of preparation, may be chosen by a person skilled in the art on the basis of his general knowledge depending on the type of composition desired.

In general, this medium may be anhydrous or aqueous. It may thus comprise an aqueous phase and/or a fatty phase.

For an application to the skin, the composition may be in particular in the form of an aqueous or oily solution; a dispersion of the lotion or serum type; emulsions of liquid or semi-liquid consistency of the milk type obtained by dispersing a fatty phase in an aqueous phase (O/W emulsion) or, conversely (W/O emulsion); suspensions or emulsions of soft consistency of the aqueous or anhydrous gel or cream type; microcapsules or microparticles; vesicular dispersions of ionic and/or nonionic type.

For an application on the hair, the composition may be in the form of aqueous, alcoholic or aqueous-alcoholic solutions; in the form of creams, gels, emulsions or mousses; in the form of aerosol compositions also comprising a propellant under pressure.

When the composition is in aqueous form, in particular in the form of an aqueous dispersion, emulsion or solution, it may comprise an aqueous phase, which may comprise water, a floral water and/or a mineral water.

The said aqueous phase may also comprise alcohols such as C₁-C₆ monoalcohols and/or polyols such as glycerol, butylene glycol, isoprene glycol, propylene glycol or polyethylene glycol.

When the composition according to the invention is in the form of an emulsion, it may optionally also comprise a surfactant, preferably in an amount of from 0.01% to 30% by weight relative to the total weight of the composition. The composition according to the invention may also comprise at least one coemulsifier which may be chosen from oxyethylenated sorbitan monostearate, fatty alcohols such as stearyl alcohol or cetyl alcohol, or fatty acid esters of polyols, such as glyceryl stearate.

The composition according to the invention may also comprise a fatty phase consisting in particular of fatty substances that are liquid at 25° C., such as volatile or non-volatile oils of animal, plant, mineral or synthetic origin; fatty substances that are solid at 25° C., such as waxes of animal, plant, mineral or synthetic origin; pasty fatty substances; gums; mixtures thereof.

The volatile oils are generally oils having, at 25° C., a saturating vapour pressure at least equal to 0.5 millibar (i.e. 50 Pa).

Among the constituents of the fatty phase which may be mentioned are:

-   -   cyclic volatile silicones containing from 3 to 8 and preferably         from 4 to 6 silicon atoms,     -   cyclocopolymers such as dimethylsiloxane/methylalkylsiloxane,     -   linear volatile silicones containing from 2 to 9 silicon atoms,     -   volatile hydrocarbon-based oils, such as isoparaffins and in         particular isododecane and fluoro oils,     -   poly(C₁-C₂₀)alkylsiloxanes and in particular those containing         trimethylsilyl end groups, among which mention may be made of         linear polydimethylsiloxanes and alkylmethylpolysiloxanes such         as cetyldimethicone (CTFA name),     -   silicones modified with aliphatic and/or aromatic groups, which         may contain fluorine, or with functional groups such as         hydroxyl, thiol and/or amine groups,     -   phenylsilicone oils,     -   oils of animal, plant or mineral origin, and in particular         animal or plant oils formed by fatty acid esters of polyols, in         particular liquid triglycerides, for example sunflower oil, corn         oil, soybean oil, marrow oil, grape seed oil, sesame oil,         hazelnut oil, apricot oil, almond oil or avocado oil; fish oils,         glyceryl tricaprocaprylate, or plant or animal oils of formula         R₁COOR₂ in which R₁ represents a higher fatty acid residue         containing from 7 to 19 carbon atoms and R₂ represents a         branched hydrocarbon-based chain containing from 3 to 20 carbon         atoms, for example purcellin oil; liquid paraffin, liquid         petroleum jelly, perhydrosqualene, wheatgerm oil, beauty-leaf         oil, sesame oil, macadamia oil, grape seed oil, rapeseed oil,         coconut oil, groundnut oil, palm oil, castor oil, jojoba oil,         olive oil or cereal germ oil; fatty acid esters; alcohols;         acetylglycerides; alkyl or polyalkyl octanoates, decanoates or         ricinoleates; fatty acid triglycerides; glycerides;     -   fluoro oils and perfluoro oils;     -   silicone gums,     -   waxes of animal, plant, mineral or synthetic origin, such as         microcrystalline waxes, paraffin, petrolatum, petroleum jelly,         ozokerite, montan wax; beeswax, lanolin and its derivatives;         candelilla wax, ouricury wax, carnauba wax, Japan wax, cocoa         butter, cork fibre wax or sugar cane wax; hydrogenated oils that         are solid at 25° C., ozokerites, fatty esters and glycerides         that are solid at 25° C.; polyethylene waxes and waxes obtained         by Fischer-Tropsch synthesis; hydrogenated oils that are solid         at 25° C.; lanolins; fatty esters that are solid at 25° C.;         silicone waxes; fluoro waxes.

In a known manner, the composition according to the invention may comprise adjuvants that are common in the field under consideration, such as hydrophilic or lipophilic gelling agents, hydrophilic or lipophilic additives, hydrophilic or lipophilic active agents, in particular cosmetic or pharmaceutical active agents, preserving agents, antioxidants, solvents, fragrances, fillers, pigments, nacres, UV screening agents, odour absorbers and colorants. Depending on their nature, these adjuvants may be introduced into the fatty phase, into the aqueous phase and/or into lipid spherules.

The nature and amount of these adjuvants may be chosen by a person skilled in the art, on the basis of his general knowledge, so as to obtain the desired presentation form for the composition. In any case, a person skilled in the art will take care to select all the optional additional compounds and/or the amount thereof, such that the advantageous properties of the composition according to invention are not, or are not substantially, adversely affected by the addition envisaged.

The cosmetic or pharmaceutical compositions according to the invention may be in particular in the form of a composition intended to care for and/or treat ulcerated areas or areas which have suffered cutaneous stress or microstress, brought about in particular by exposure to UV and/or by coming into contact with an irritant product.

Thus, the compositions according to the invention may be in particular in the form:

-   -   of a care, treatment, cleansing or protective product for facial         or body skin, including the scalp, such as a care composition         (moisturizing day or night composition) for the face or the         body; an anti-wrinkle or anti-ageing composition for the face; a         matt-effect composition for the face; a composition for         irritated skin; a make-up-removing composition; a body milk, in         particular a moisturizing and optionally after-sun body milk;     -   of an anti-sun composition, an artificial tanning (self-tanning)         composition or an after-sun care composition;     -   of a haircare composition, and in particular an anti-sun cream         or gel; a scalp care composition, in particular to prevent hair         loss or to promote regrowth of the hair; an anti-parasite         shampoo;     -   of a make-up product for the skin of the face, the body or the         lips, such as a foundation, a tinted cream, a blusher, an eye         shadow, a free or compact powder, a concealer stick, a cover         stick, a lipstick or a lipcare product;     -   of an oral hygiene product such as a toothpaste or an oral         rinsing lotion.

The compositions according to the invention find a preferred application as a facial skincare composition, of anti-wrinkle or anti-ageing type, and as an anti-sun or after-sun composition.

A subject of the present invention is also a cosmetic treatment process for facial or body skin, including the scalp, in which a cosmetic composition comprising an effective amount of at least one compound of formula (I) is applied to the skin, left in contact with the skin and then optionally rinsed off.

The cosmetic treatment process of the invention may be carried out in particular by applying the cosmetic compositions as defined above, according to the usual technique for using these compositions. For example: application of creams, gels, sera, lotions, make-up-removing milks or anti-sun compositions to the skin or to dry hair; application of a scalp lotion to wet hair; application of toothpaste to the gums;

The invention is illustrated in further detail in the examples which follow.

EXAMPLE 1 Preparation of ethyl {2-[acetyl(3-trifluoromethyl-phenyl)amino]-3-methylbutyrylamino}acetate of formula

0.63 ml of isobutyraldehyde and 1 ml of trifluoromethylamine (1.15 eq) are mixed together in 15 ml of methanol, with stirring. The mixture is left to react for 15 minutes at 20° C., 0.46 ml of acetic acid (1.15 eq) is then added and the mixture is left to react for 10 minutes at 20° C. 0.8 ml of 95% ethyl isocyanoacetate (1 eq) is then added and the mixture is left to react for 48 hours at 20° C.

The reaction medium is concentrated on a rotovapor and the residue is purified on a column of silica (eluent: 3/7 heptane/ethyl acetate: Rf=0.5).

2.45 g of compound are obtained in the form of a waxy solid, equivalent to a yield of 91%.

¹H NMR (200 MHz; CDCl₃) δ ppm: 0.9 (6H;q), 1.3. (3H;t), 1.8 (3H;s), 2.3 (1H;m), 4.0 (2H,q), 4.2 (2H;q), 4.4 (2H;d), 7.3 (1H;t), 7.5 (4H;m)

EXAMPLE 2 Preparation of {2-[acetyl(3-trifluoromethyl-phenyl)amino]-3-methylbutyrylamino}acetic acid of formula

2 g of compound prepared in Example 1 are dissolved in 30 ml of acetone. 30 ml of 2N sodium hydroxide are added and the mixture is left to react for 6 hours at 20° C. The reaction medium is concentrated on a rotovapor. The residual aqueous phase is acidified to pH 2 by adding concentrated HCl and the resulting mixture is then extracted with CH₂Cl₂.

The organic phase is concentrated to dryness after drying over sodium sulphate. A residue is obtained, which is dissolved with an aqueous 10% basic ethanol mixture and is then reacidified to pH 2 with concentrated HCl. It is re-extracted with CH₂Cl₂ and the organic phase is dried over sodium sulphate, filtered and concentrated to dryness under vacuum on a rotovapor.

1.3 g of compound are obtained in the form of a slightly light brown solid, equivalent to a yield of 70%.

¹H NMR (200 MHz; DMSO) δ ppm: 0.9 (6H;q), 3.7 (2H;m), 1.8 (4H;m), 4.8 (2H;d), 7.6 (4H,m), 8.4 (1H;t), 12.5 (1H;s)

EXAMPLE 3

The in vitro anti-elastase activity of compounds according to the invention with respect to human leukocyte elastase (HLE) was determined.

The test is carried out in the following way: A substrate Me-OSAAPV-p-NA (methyl-O-succinate alanine alanine proline valine-p-nitroanilide) on which is applied HLE (40 milliunits per ml) and 0.1% of the test compound is incubated at 37° C. for 60 minutes.

The percentage inhibition of the control elastase activity is then determined by spectrophotometry.

The test compounds are as follows:

-   Compound A:     12-[acetyl(3-trifluoromethylphenyl)amino]-3-methylbutyrylamino)acetic     acid -   Compound B: ethyl [2-{benzyl[(diethoxyphosphoryl)-acetyl]amino}-+ b     3-methylbutyrylamino]acetate -   Compound C: [2-(acetylbenzylamino)-3-methylbutyrylamino]acetic acid -   Compound D: ethyl     [2-(acetylbenzylamino)-3-methylbutyrylamino]acetate

The following results are obtained: % inhibition of the Compound (concentration: control elastase 0.1%) activity Compound A 67% Compound B 17% Compound C 20% Compound D 13%

The percentage inhibition of the control elastase activity is determined in the same way for compound A, at different concentrations.

The following results are obtained: % inhibition of the control elastase Concentration of compound A activity 0.01% 53% 0.05% 50%  0.1% 68%  0.2% 68%

Compound A thus induces a strong inhibition of the elastase activity, even in a small amount.

EXAMPLE 4

The ex vivo activity of the compound of Example 2 was evaluated on surviving human skin treated with human leukocyte elastase (HLE).

The test is carried out in the following way:

Fresh sections of human skin, obtained from 2 different donors, are treated for 2 hours at 20° C. with 20 μl of buffer solution (pH 7.4) optionally comprising 10 μg/ml of HLE and optionally 0.1% of the test compound, optionally predissolved in ethanol.

The elastic fibres are stained blue with (+)-catechin and morphometrically quantified by computer-assisted image analysis. The percentage of average dermal surface area occupied by the elastic fibres is thus evaluated.

The following results are obtained: % of surface area occupied by the elastic fibres Skin 1 Skin 2 Control (untreated  12.7% 15.25% skin) Skin treated with  4.85% 6.85% HLE Skin treated with 13.95% 11.85% HLE + compound of Example 2

It is thus found that the compound according to the invention generates a significant protection of the skins with respect to the destruction of the elastic fibres which is induced by elastase.

EXAMPLE 5

The ex vivo activity of the compound of Example 2 was evaluated on surviving human skin treated with human leukocyte elastase (HLE).

The test is carried out in the following way:

Fragments of normal human skin obtained from three different donors are placed in inserts positioned in culture wells. Culture medium supplemented with antibiotics is placed in the bottom of the wells. A passage is carried out by slow diffusion between the two compartments by means of a porous membrane (pore size: 12 μm).

The culture medium is freshened every three days.

0.5 μg of HLE per ml of culture medium is optionally added to the skin fragments.

5 μl of the test compound, predissolved at a concentration of 0.2% by weight in ethanol, is also added every two days.

The skins are kept alive for 10 days at 37° C.

The elastic fibres are stained blue with (+)-catechin and morphometrically quantified by computer-assisted image analysis. The percentage of average dermal surface area occupied by the elastic fibres is thus evaluated.

The following results are obtained: % of surface area occupied by the elastic fibres Control (untreated skin) 7.4% Skin treated with HLE 5.1% Skin treated with HLE + compound 7.1% of Example 2

It is thus found that the compound according to the invention generates a significant protection of the skins with respect to the destruction of the elastic fibres which is induced by elastase.

EXAMPLE 6

The activity of the compound of Example 2 on surviving human skin irradiated with UVA (8 J/cm²) was evaluated.

The test is carried out in the following way:

Fragments of normal human skin obtained from four different donors are placed in inserts positioned in culture wells. Culture medium supplemented with antibiotics is placed in the bottom of the wells. A passage is carried out by slow diffusion between the two compartments by means of a porous membrane (pore size: 12 μm).

The culture medium is freshened every three days.

5 μl of the test compound, predissolved at a concentration of 0.2% in ethanol, is added to the skin fragments every two days.

The skins are kept alive for 7 days at 37° C.

The skins are irradiated once at 8 J/cm² (Vilbert-Lourmat RMX-3W lamp).

The elastic fibres are stained blue with (+)-catechin and morphometrically quantified by computer-assisted image analysis. The percentage of average dermal surface area occupied by the elastic fibres is thus evaluated.

The following results are obtained: Morphometric Morphometric analysis of the analysis of elastic fibres the collagen (superficial (superficial dermis) dermis) Untreated skin 6.75% 87% Skin treated with  3.9% 81% UVA (8 J/cm²) Skin treated with  6.8% 92% UVA (8 J/cm²) + compound

It is found that the compound according to the invention does indeed have activity with respect to the degradation of elastic fibres in the superficial dermis of skin irradiated with UVA.

This compound also has an adequate effect on protecting collagen.

EXAMPLE 7 Composition for Topical Application

The emulsion below is prepared in a conventional manner (% by weight): Compound of Example 1   1% Propylene glycol isostearate   13% Polyethylene glycol (8 EO)   5% Propylene glycol   3% Pentylene glycol   3% Glyceryl stearate and polyethylene glycol   5% stearate (100 EO) Oxyethylenated sorbitan monostearate (20 EO)  0.5% Oxyethylenated (20 EO) oxypropylenated (5 PO)   1% cetyl alcohol Gelling agents  0.5% C₁₂-C₁₅ alkyl benzoates   4% Ethanol   3% Sodium hydroxide 0.12% Preserving agents qs Water qs 100%

EXAMPLE 8 Facial Care Cream

The oil-in-water emulsion below is prepared in a conventional manner (% by weight): Compound of Example 2   1% Glyceryl stearate   2% Polysorbate 60 (Tween 60 ® sold by the company   1% ICI) Stearic acid 1.4% Triethanolamine 0.7% Carbomer 0.4% Liquid fraction of karite butter  12% Perhydrosqualene  12% Antioxidant qs Fragrance qs Preserving agent qs Water qs 100%

EXAMPLE 9 Facial Milk

The milk below is prepared in a conventional manner (% by weight): Liquid petroleum jelly   7% Compound of Example 2   1% Glyceryl monostearate, polyethylene glycol   3% stearate (100 EO) Carboxyvinyl polymer 0.4% Stearyl alcohol 0.7% Soybean proteins   3% NaOH 0.4% Preserving agent qs Water qs 100%

EXAMPLE 10 Hair Lotion

The lotion below is prepared in a conventional manner (% by weight): Compound of Example 1  1% Propylene glycol 23% Ethanol 55% Water qs 100%

This lotion may be applied to the scalp of alopecic individuals, to prevent the effects of UV, before and/or after exposure to the sun.

EXAMPLE 11 Lotion for Preventing Hair Loss

The lotion below is prepared in a conventional manner (% by weight): Compound of Example 2   1% Propylene glycol  23% Ethanol  55% Aminexil 1.5% Water qs 100%

This lotion for preventing hair loss may be applied to the scalp of alopecic individuals. 

1-13. (canceled)
 14. A composition comprising, in a physiologically acceptable medium, at least one compound chosen from compounds of formula (I):

wherein: Y is chosen from O and S, R₁ is chosen from: (i) hydrogen; (ii) linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —P(O)—(OR)₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; and (iii) radicals chosen from —OR; —NH₂; —NHR; —NRR′; —NH—COR; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; R₂ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; R₃ is a radical chosen from those of formulae (II) and (III): -A-C₆H_((5-y))—B_(y)  (II) —C₆H_((5-y′))—B_(y)′  (III) wherein: y is an integer ranging from 0 to 5 and y′ is an integer ranging from 1 to 5; A is chosen from linear and branched, saturated and unsaturated divalent hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; B, which may be identical or different, is chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR, and linear and branched, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen, or even perhalogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; X is a radical chosen from —OH, —OR₄, —NH₂, —NHR₄, —NR₄R₅, —SR₄, —COOR₄ and —COR₄; wherein R₄ and R₅, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; the said radicals R₄ and R₅ optionally forming, together with N in the —NR₄R₅, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; the mineral acid and organic acid salts thereof, and the optical isomers thereof, in isolated form and as a racemic mixture, with the exception of the following compounds: N-acetylglycyl-N-(benzyl)-DL-valylglycine tert-butyl ester; N-acetylglycyl-N-(2-nitrobenzyl)-DL-valylglycine tert-butyl ester; and N-acetylglycyl-N-(2,4-dimethyloxybenzyl)-DL-valylglycine tert-butyl ester; wherein the composition is in a form chosen from cosmetic and pharmaceutical compositions for at least one of the care and treatment of at least one area chosen from ulcerated areas, areas which have suffered cutaneous stress, and areas which have suffered microstress.
 15. The composition according to claim 14, wherein the at least one area chosen from ulcerated areas, areas that have suffered cutaneous stress, and areas that have suffered microstress, is an area that has suffered from at least one of exposure to UV radiation and contact with an irritant product.
 16. A composition comprising, in a physiologically acceptable medium, at least one compound chosen from compounds of formula (I):

wherein: Y is chosen from O and S, R₁ is chosen from: (i) hydrogen; (ii) linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —P(O)—(OR)₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; and (iii) radicals chosen from —OR; —NH₂; —NHR; —NRR′; —NH—COR; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; R₂ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; R₃ is a radical chosen from those of formulae (II) and (III): -A-C₆H_((5-y))—B_(y)  (II) —C₆H_((5-y′))—B_(y)′  (III) wherein: y is an integer ranging from 0 to 5 and y′ is an integer ranging from 1 to 5; A is chosen from linear and branched, saturated and unsaturated divalent hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; B, which may be identical or different, is chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR, and linear and branched, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen, or even perhalogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; X is a radical chosen from —OH, —OR₄, —NH₂, —NHR₄, —NR₄R₅, —SR₄, —COOR₄ and —COR₄; wherein R₄ and R₅, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; the said radicals R₄ and R₅ optionally forming, together with N in the —NR₄R₅, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; the mineral acid and organic acid salts thereof, and the optical isomers thereof, in isolated form and as a racemic mixture, with the exception of the following compounds: N-acetylglycyl-N-(benzyl)-DL-valylglycine tert-butyl ester; N-acetylglycyl-N-(2-nitrobenzyl)-DL-valylglycine tert-butyl ester; and N-acetylglycyl-N-(2,4-dimethyloxybenzyl)-DL-valylglycine tert-butyl ester; wherein the composition is in a form chosen from: care, treatment, cleansing and protective products for facial and body skin; anti-wrinkle and anti-ageing compositions; matte-effect compositions; compositions for irritated skin; make-up removing compositions; and body milks; anti-sun compositions, artificial tanning (self-tanning) compositions and after-sun care compositions; haircare compositions and scalp care compositions; make-up products for the skin of the face, body and lips; and oral hygiene products.
 17. The composition according to claim 16, wherein the body skin is the scalp.
 18. The composition according to claim 16, wherein the care, treatment, cleansing and protective products are chosen from moisturizing day compositions and moisturizing night compositions for the skin.
 19. The composition according to claim 16, wherein the haircare compositions are in a form chosen from anti-sun creams and gels.
 20. The composition according to claim 17, wherein the scalp care compositions are compositions for at least one of prevention of hair loss, promotion of hair growth, and promotion of hair regrowth.
 21. The composition according to claim 16, wherein the make-up products are in a form chosen from foundations, tinted creams, blushers, eyeshadows, free and compact powders, concealer sticks, cover sticks, lipsticks, and lipcare products.
 22. The composition according to claim 16, wherein the oral hygiene products are in a form chosen from toothpastes and oral rinsing lotions.
 23. The composition according to claim 16, wherein said body milks are chosen from moisturizing body milks and after-sun body milks.
 24. A composition comprising, in a physiologically acceptable medium, at least one compound chosen from compounds of formula (I):

wherein: Y is chosen from O and S, R₁ is chosen from: (i) hydrogen; (ii) linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —P(O)—(OR)₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; and (iii) radicals chosen from —OR; —NH₂; —NHR; —NRR′; —NH—COR; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; R₂ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; R₃ is a radical chosen from those of formulae (II) and (III): -A-C₆H_((5-y))—B_(y)  (II) —C₆H_((5-y′))—B_(y)′  (III) wherein: y is an integer ranging from 0 to 5 and y′ is an integer ranging from 1 to 5; A is chosen from linear and branched, saturated and unsaturated divalent hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; B, which may be identical or different, is chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR, and linear and branched, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen, or even perhalogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; X is a radical chosen from —OH, —OR₄, —NH₂, —NHR₄, —NR₄R₅, —SR₄, —COOR₄ and —COR₄; wherein R₄ and R₅, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; the said radicals R₄ and R₅ optionally forming, together with N in the —NR₄R₅, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; the mineral acid and organic acid salts thereof, and the optical isomers thereof, in isolated form and as a racemic mixture, with the exception of the following compounds: N-acetylglycyl-N-(benzyl)-DL-valylglycine tert-butyl ester; N-acetylglycyl-N-(2-nitrobenzyl)-DL-valylglycine tert-butyl ester; and N-acetylglycyl-N-(2,4-dimethyloxybenzyl)-DL-valylglycine tert-butyl ester; wherein the composition is in a form chosen from facial skincare compositions, anti-wrinkle compositions, anti-ageing compositions, anti-sun compositions, and after-sun compositions.
 25. A method of treating at least one sign of skin ageing, comprising applying to the skin at least one compound chosen from compounds of formula (I):

wherein: Y is chosen from O and S, R₁ is chosen from: (i) hydrogen; (ii) linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —P(O)—(OR)₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; and (iii) radicals chosen from —OR; —NH₂; —NHR; —NRR′; —NH—COR; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; R₂ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; R₃ is a radical chosen from those of formulae (II) and (III): -A-C₆H_((5-y))—B_(y)  (II) —C₆H_((5-y′))—B_(y)′  (III) wherein: y is an integer ranging from 0 to 5 and y′ is an integer ranging from 1 to 5; A is chosen from linear and branched, saturated and unsaturated divalent hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; B, which may be identical or different, is chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR, and linear and branched, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen, or even perhalogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; X is a radical chosen from —OH, —OR₄, —NH₂, —NHR₄, —NR₄R₅, —SR₄, —COOR₄ and —COR₄; wherein R₄ and R₅, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; the said radicals R₄ and R₅ optionally forming, together with N in the —NR₄R₅, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; the mineral acid and organic acid salts thereof, and the optical isomers thereof, in isolated form and as a racemic mixture, with the exception of the following compounds: N-acetylglycyl-N-(benzyl)-DL-valylglycine tert-butyl ester; N-acetylglycyl-N-(2-nitrobenzyl)-DL-valylglycine tert-butyl ester; and N-acetylglycyl-N-(2,4-dimethyloxybenzyl)-DL-valylglycine tert-butyl ester.
 26. The method according to claim 25, wherein the skin is chosen from facial skin and body skin.
 27. The method according to claim 25, wherein the ageing is chosen from chronobiological ageing and light-induced ageing.
 28. The method according to claim 25, wherein the ageing is generated by at least one of a reduction in the elasticity of the skin and a degradation of the collogen in the structure of the tissues.
 29. A method of treating at least one sign of skin ageing, comprising applying to the skin a composition comprising, in a physiologically acceptable medium, at least one compound chosen from compounds of formula (I):

wherein: Y is chosen from O and S, R₁ is chosen from: (i) hydrogen; (ii) linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —P(O)—(OR)₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; and (iii) radicals chosen from —OR; —NH₂; —NHR; —NRR′; —NH—COR; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; R₂ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; R₃ is a radical chosen from those of formulae (II) and (III): -A-C₆H_((5-y))—B_(y)  (II) —C₆H_((5-y′))—B_(y)′  (III) wherein: y is an integer ranging from 0 to 5 and y′ is an integer ranging from 1 to 5; A is chosen from linear and branched, saturated and unsaturated divalent hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; B, which may be identical or different, is chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR, and linear and branched, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen, or even perhalogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; X is a radical chosen from —OH, —OR₄, —NH₂, —NHR₄, —NR₄R₅, —SR₄, —COOR₄ and —COR₄; wherein R₄ and R₅, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; the said radicals R₄ and R₅ optionally forming, together with N in the —NR₄R₅, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; the mineral acid and organic acid salts thereof, and the optical isomers thereof, in isolated form and as a racemic mixture, with the exception of the following compounds: N-acetylglycyl-N-(benzyl)-DL-valylglycine tert-butyl ester; N-acetylglycyl-N-(2-nitrobenzyl)-DL-valylglycine tert-butyl ester; and N-acetylglycyl-N-(2,4-dimethyloxybenzyl)-DL-valylglycine tert-butyl ester.
 30. The method according to claim 29, wherein the skin is chosen from facial skin and body skin.
 31. The method according to claim 29, wherein the ageing is chosen from chronobiological ageing and light-induced ageing.
 32. The method according to claim 29, wherein the ageing is generated by at least one of a reduction in the elasticity of the skin and a degradation of the collogen in the structure of the tissues.
 33. A method for treating at least one type of skin chosen from skin with wrinkles and fine lines, wizened skin, skin lacking elasticity, skin lacking tone, skin suffering from a thinned dermis, skin suffering from degradation of collagen fibres, flaccid skin, thinned skin, and skin suffering from internal degradation following exposure to ultraviolet radiation, wherein the method comprises applying to the skin at least one compound chosen from compounds of formula (I):

wherein: Y is chosen from O and S, R₁ is chosen from: (i) hydrogen; (ii) linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —P(O)—(OR)₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; and (iii) radicals chosen from —OR; —NH₂; —NHR; —NRR′; —NH—COR; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; R₂ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; R₃ is a radical chosen from those of formulae (II) and (III): -A-C₆H_((5-y))—B_(y)  (II) —C₆H_((5-y′))—B_(y)′  (III) wherein: y is an integer ranging from 0 to 5 and y′ is an integer ranging from 1 to 5; A is chosen from linear and branched, saturated and unsaturated divalent hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; B, which may be identical or different, is chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR, and linear and branched, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen, or even perhalogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; X is a radical chosen from —OH, —OR₄, —NH₂, —NHR₄, —NR₄R₅, —SR₄, —COOR₄ and —COR₄; wherein R₄ and R₅, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; the said radicals R₄ and R₅ optionally forming, together with N in the —NR₄R₅, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; the mineral acid and organic acid salts thereof, and the optical isomers thereof, in isolated form and as a racemic mixture, with the exception of the following compounds: N-acetylglycyl-N-(benzyl)-DL-valylglycine tert-butyl ester; N-acetylglycyl-N-(2-nitrobenzyl)-DL-valylglycine tert-butyl ester; and N-acetylglycyl-N-(2,4-dimethyloxybenzyl)-DL-valylglycine tert-butyl ester.
 34. A method for treating at least one type of skin chosen from skin with wrinkles and fine lines, wizened skin, skin lacking elasticity, skin lacking tone, skin suffering from a thinned dermis, skin suffering from degradation of collagen fibres, flaccid skin, thinned skin, and skin suffering from internal degradation following exposure to ultraviolet radiation, wherein the method comprises applying to the skin a composition comprising, in a physiologically acceptable medium, at least one compound chosen from compounds of formula (I):

wherein: Y is chosen from O and S, R₁ is chosen from: (i) hydrogen; (ii) linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —P(O)—(OR)₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; and (iii) radicals chosen from —OR; —NH₂; —NHR; —NRR′; —NH—COR; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; R₂ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; R₃ is a radical chosen from those of formulae (II) and (III): -A-C₆H_((5-y))—B_(y)  (II) —C₆H_((5-y′))—B_(y)′  (III) wherein: y is an integer ranging from 0 to 5 and y′ is an integer ranging from 1 to 5; A is chosen from linear and branched, saturated and unsaturated divalent hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; B, which may be identical or different, is chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR, and linear and branched, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 18 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen, or even perhalogen); —CN; —COOR; —COR; —NO₂; and —SO₂—OR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; X is a radical chosen from —OH, —OR₄, —NH₂, —NHR₄, —NR₄R₅, —SR₄, —COOR₄ and —COR₄; wherein R₄ and R₅, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, optionally substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR; —O—COR; —SH; —SR; —S—COR; —NH₂; —NHR; —NRR′; —NH—COR; -Hal (halogen); —CN; —COOR; and —COR; wherein R and R′, which may be identical or different, are each chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen, the said radicals R and R′ optionally forming, together with N in the —NRR′, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; the said radicals R₄ and R₅ optionally forming, together with N in the —NR₄R₅, a 5- or 6-membered carbon-based ring which may further comprise at least one hetero atom chosen from O, N and S in the ring, and/or which may be substituted with 1 to 5 groups, which may be identical or different, chosen from —OH; —OR″; —O—COR″; —SH; —SR″; —S—COR″; —NH₂; —NHR″; —NH—COR″; -Hal (halogen); —CN; —COOR″; and —COR″; wherein R″ is chosen from linear, branched and cyclic, saturated and unsaturated hydrocarbon-based radicals containing from 1 to 6 carbon atoms, which are optionally substituted with at least one halogen; the mineral acid and organic acid salts thereof, and the optical isomers thereof, in isolated form and as a racemic mixture, with the exception of the following compounds: N-acetylglycyl-N-(benzyl)-DL-valylglycine tert-butyl ester; N-acetylglycyl-N-(2-nitrobenzyl)-DL-valylglycine tert-butyl ester; and N-acetylglycyl-N-(2,4-dimethyloxybenzyl)-DL-valylglycine tert-butyl ester.
 35. The composition according to claim 16, wherein the composition for application to the skin is in a form chosen from aqueous and oily solutions; dispersions; emulsions of liquid and semi-liquid consistency obtained by dispersing a fatty phase in an aqueous phase (O/W emulsions) and (W/O emulsions); suspensions and emulsions, aqueous and anhydrous gels and creams; microcapsules and microparticles; and ionic and non-ionic vesicular dispersions.
 36. The composition according to claim 16, wherein the composition for application to hair is in a form chosen from aqueous, alcoholic and aqueous-alcoholic solutions; creams, gels, emulsions and mousses; and aerosol compositions comprising a propellant under pressure. 